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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 5 December 2010 by dana1981

One of the largest uncertainties in global climate models (GCMs) is the response of clouds in a warming world. Determining which types of cloud cover will increase or decrease, whether that will result in a net positive or negative feedback, and how large the feedback will be, are major challenges. The variation in global climate sensitivity among GCMs is largely attributable to differences in cloud feedbacks, and feedbacks of low-level clouds in particular.

For climate scientists who are skeptical that anthropogenic greenhouse gas emissions will cause a dangerous amount of warming, such as Richard Lindzen and Roy Spencer, their skepticism hinges mainly on this cloud cover uncertainty. They tend to believe that as the planet warms, low-level cloud cover will increase, thus increasing planetary albedo (overall reflectiveness of the Earth), offsetting the increased greenhouse effect and preventing a dangerous level of global warming from occurring.

Recently some studies have examined the cloud feedback specifically in the eastern Pacific region. Stowasser et al. (2006) found that:

"In terms of the sensitivity of the global-mean surface temperature, almost all the differences among the models could be attributed to differences in the shortwave cloud feedbacks in the tropical and subtropical regions."

In order to evaluate this uncertainty, Lauer et al. (2010) used 16 GCMs and the International Pacific Research Center (IPRC) Regional Atmospheric Model (iRAM) described in Lauer et al. (2009) to simulate clouds and cloud–climate feedbacks in the tropical and subtropical eastern Pacific region. To investigate cloud–climate feedbacks in iRAM, the authors ran several global warming scenarios with boundary conditions appropriate for late twenty-first-century conditions (specifically, warming signals based on IPCC AR4 SRES A1B simulations).

Figure 1 shows the results of the 16 GCMs, iRAM (bottom center), and satellite observations (bottom right). A clearer version of this figure can be seen in Figure 1 on Page 6 of Lauer et al. (2010).

"The authors find that the simulation of the present-day mean cloud climatology for this region in the GCMs is very poor and that the cloud–climate feedbacks vary widely among the GCMs. By contrast, iRAM simulates mean clouds and interannual cloud variations that are quite similar to those observed in this region."

Thus the study shows that that iRAM simulates recently observed cloud cover changes in this the eastern Pacific more accurately than the GCMs, and iRAM also successfully simulates the main features of the observed interannual variation of clouds in this region, including the evolution of the clouds through the El Niño Southern Oscillation (ENSO) cycle. Given these conclusions, the logical assumption is that iRAM will also model future cloud cover changes more accurately. Operating under this assumption, the authors conclude as follows.

"All the global warming cases simulated with iRAM show a distinct reduction in low-level cloud amount, particularly in the stratocumulus regime, resulting in positive local feedback parameters in these regions in the range of 4–7 W m-2 K-1....The GCM feedbacks vary from -1.0 to +1.3 W m-2 K-1, which are all less than the +1.8 to +1.9 W m-2 K-1 obtained in the comparable iRAM simulations. The iRAM results by themselves cannot be connected definitively to global climate feedbacks, but we have shown that among the GCMs the cloud feedbacks averaged over 30°S–30°N and the equilibrium global climate sensitivity are both correlated strongly with the east Pacific cloud feedback. To the extent that iRAM results for cloud feedbacks in the east Pacific are credible, they provide support for the high end of current estimates of global climate sensitivity."

Lauer et al. (2010) is not alone in its conclusion that the low-level cloud cover feedback will be positive. Other studies analyzing satellite data from the International Satellite Cloud Climatology Project (ISCCP), the Advanced Very High Resolution Radiometer (AVHRR), and the Clouds and the Earth’s Radiant Energy System (CERES) such as Chang and Coakley (2007) and Eitzen et al. (2008) have indicated that cloud optical depth of low marine clouds might be expected to decrease with increasing temperature. This suggests a positive shortwave cloud–climate feedback for marine stratocumulus decks.

In another recent paper, Clement et al. (2009) analyzed several decades of ship-based observations of cloud cover along with more recent satellite observations, with a focus on the northeastern Pacific. They found that there is a negative correlation between cloud cover and sea surface temperature apparent on a long time scale—again suggesting a positive cloud-climate feedback in this region.

In short, while much more research of the cloud-climate feedback is needed, the evidence is stacking up against those who argue that climate sensitivity is low due to a strongly negative cloud feedback.

@Eric (skeptic): you are exaggerating the impact of TSI and galactic cosmic rays.

Also, what do you mean by "obviously nature is damping man's additional CO2"?

The problem with your theory is that it is not confirmed by oservation. There is no indication that external factors such as TSI or GCR could overcome AGW. Until you have actual evidence supporting your theory, we'll have to continue assuming it is very unlikely.

Eric #50, you've made a number of incorrect statements. Firstly, that CO2 has been a slow feedback at times in the past does not mean it must always be a slow feedback - that's a basic logical fallacy. Besides which, it's not currently a feedback, it's a forcing.

Secondly, the planet is already warming at nearly 2°C per century, so it's already not acting slowly.

Third, while future changes in solar and other natural factors are hard to predict, that's not really relevant. Maybe the Sun will be a positive forcing, maybe a negative one, maybe a neutral one. What we do know is that greenhouse gases are a large positive forcing which will continue to have a warming effect.

Fourth, permafrost is already melting and releasing methane, thus you're once again contradicting empirical observations by claiming this feedback will take centuries.

Fifth, there's not much question that water vapor will be a positive feedback, the only real question is how strong that feedback will be.

Sixth, it's the argument of Lindzen and Spencer etc. that a negative cloud feedback will prevent significant warming. I didn't make it up - I was addressing their argument.

And seventh, the galactic cosmic ray influence on the global climate has been demonstrated to be minimal.

archiesteel, TSI is not a very useful measurement. UV and other components are more useful since UV modulates blocking and blocking modulates sensitivity. By damping I meant that about 1/2 of man's contribution of CO2 to the atmosphere is absorbed by nature. Since I can't predict solar and GCR, I can't say whether it will mitigate or worsen AGW.

Dana, thanks for addressing my assertions, hopefully I can clarify and maybe some are still wrong after I do. I definitely consider CO2 as a forcing, but it has also been considered a feedback in various threads including the paleo sensitivity threads where it is (IMO incorrectly) considered to be the primary feedback, so that's why I mentioned that. The recent warming (2C per century peak rate) has had many short term fluctuations, hardly representative of the long term sensitivity. I agree with your third point, but it consists of a modest warming effect from GHG before considering sensitivity. Methane varies greatly in the short term and no long term sensitivity conclusions can be made. I agree with your fifth point because water vapor will increase on average with evenness being the big unknown.

My argument is a little different Lindzen and Spencer as I see a greater effect from external factors, not in their models and not in their critics models, on clouds. You previously dismissed GCR in the thread I linked to only by hypothesizing it as the only factor, comparing the linear trend with linear temperature trend and seeing no correlation. But the only possible conclusion is that GCR did not exceed other factors in the last 30 years, not that GCR has no influence. It clearly has a substantial influence on clouds, but those cloud changes do not directly control temperature but mostly weather. In the past 30 years, other factors, both terrestrial and not, have had a larger influence on weather. The reaction of weather to these factors is what sensitivity is.

Great post and thanks for covering this important topic. I was hoping SS was going to cover the Lauer et al. (2010) paper and you did not disappoint.

Could the "skeptics" please tell us when this supposed (and mysterious) significant negative cloud feedback is going to kick in? It has not kicked in, and the only reliable, coherent data and studies argue against a significant negative feedback.

The long term warming continues in the 0.15 to 0.20 C per decade range, as per RSS data and as per Hansen et al's latest paper.

"archiesteel, TSI is not a very useful measurement. UV and other components are more useful since UV modulates blocking and blocking modulates sensitivity. By damping I meant that about 1/2 of man's contribution of CO2 to the atmosphere is absorbed by nature."

How does this affect ("modulate") sensitivity? By definition, sensitivity is related to the amount of CO2 in the atmosphere, not to the amount emitted by humans (or other sources). In other words after consumption by plant life, absorption by oceans, etc has been taken into account.

#57 archiesteel, there is no GCR counter to AGW in the past 30 years, but there could certainly be GCR warming in the late 20th century or possibly recent GCR-based cooling offsetting some warming. But GCR is not the story here, it is all the factors spelled out in How-we-know-the-sun-isnt-causing-global-warming.html which constantly fluctuate and add and subtract from the AGW warming. By not including them in either paleo studies or in the models that create clouds, we can't say anything about their effect on sensitivity. They can't be ignored just because they were canceled out over the past 30 years.

#56 dhogaza, I should probably not have appropriated the term "modulate". Those statements were answers to two different questions. Natural "damping" of CO2 simply means that CO2 is only a forcing and will not be a positive feedback in any time scale we care about (contrary to On-temperature-and-CO2-in-the-past.html where the charts are missing the other factors that control sensitivity)

On the other point, sensitivity is a function of warming from CO2, not the amount of CO2. There is no physical link from the amount of CO2 to the amount of water vapor (or any other postulated feedback parameter) except through CO2 warming. Sensitivity is not a constant although it can be averaged over time and over the earth usually by oversimplifying. A function for sensitivity could be something like delta T = CO2 warming times A where A is the amplification determined by how the weather changes both in response to the warming and how the weather changes in response to external factors (those factors are not necessarily other forcings). "A" would also include increases in water vapor.

Eric, I disagree with your statement that GCR flux "clearly has a substantial influence on clouds". If you go back to my GCR article, I addressed this issue. A number of recent studies have demonstrated that GCRs actually appear to play a very minor role in cloud formation.

Also as dhogaza noted in comment #56, sensitivity is measured as the response to increasing atmospheric CO2, not to increasing CO2 emissions. The sensitivity to a doubling of atmospheric CO2, which we are currently projected to reach (doubled from the pre-industrial level of 280 ppm) by mid-to-late century, is 2-4.5°C. This accounts for absorption of anthropogenic emissions by the biosphere.

And like archiesteel, I've seen no convincing evidence that UV plays a significant role in climate sensitivity. I have seen evidence that it can influence local weather patterns, but that's a different subject, since sensitivity pertains to *global* temperature changes.

#54: "the only possible conclusion is that GCR did not exceed other factors in the last 30 years, not that GCR has no influence. It clearly has a substantial influence on clouds"

Seems like a false dichotomy to me. I second archiesteel (#57); this idea that GCRs will somehow come to the rescue -- and that won't be until the next solar min if ever -- is pure moonshine.

Here is the GCR graph from the reference I cited in #26.

Neither the recent peak in GCRs or the prior 1997-98 peak did anything to modulate or moderate or block or unblock temperatures. We're still waiting for that 'substantial influence' to make itself known. This is starting to sound like a musical. With my apologies:
And where are the clouds?
There ought to be clouds.
Well, maybe next year.

Dana, thanks for the replies. I agree that increasing CO2 is the correct input to the sensitivity calculation, not emissions, sorry for the confusion (I went on a tangent). I will read and comment at the GCR thread regarding that topic.

Sensitivity has to be calculated from the response to local temperature changes since that it the only physical mechanism for such responses. For example an increase in sensitivity could come from increases in arctic WV which come from CO2 warming. A further rise in sensitivity could come from the earlier snow melt (reduced albedo) from that warming, or a cloud change or something else. The parameters and effects are all local and then integrated into local and then global averages. Thus the local effect from UV-induced weather pattern change in your example is very relevant. This is because the water vapor feedback from CO2 forcing is different (e.g. lower UV -> blocking pattern -> large areas of subsidence -> lower UT WV from a given amount of CO2 warming). When a number of local blocking effects are integrated over the planet, that changes the sensitivity for the planet.

Having read this entire thread, it seems like Camburn has summed up the "skeptical" response pretty well @42: "I feel very lucky." Plenty of good science says that clouds may not make things better, and may even make things worse. But what of it? "I feel very lucky."

Which is easy enough to say, when you're unlikely to suffer the worst consequences of being wrong. That's what makes the "skeptical" position morally untenable, IMO.

Phila:
I feel very lucky for numerous reasons concerning climate.
1. Statistically, and this is important unless you want to throw statistical analysis out with the wash, we have not warmed for the past 15 years.
2. Prof Trenbeth talks about the missing heat. I will have to dig to find the paper that I read in the past few months concerning this. The observations at TOA are not what the models show should be happening.
3. Global cloud cover seems to have shifted upwards from a long downward spiral. This would help explain the lack of stastistical warming for the past 15 years. I don't know why it has done this, but it has.
http://mclean.ch/climate/Cloud_global.htm

00

Response:"Statistically... we have not warmed for the past 15 years."

This issue is examined in detail at "Phil Jones says no global warming since 1995". The HadCRUT record shows around 93% chance of a warming trend - while this falls a shade below the 95% threshhold to be labelled statistically significant, to move from 93% chance of warming to "we have not warmed for the past 15 years" is a gross distortion.

Statistically speaking, the NASA GISS temperature record does show significant warming since 1995. The European ECMWF reanalysis also shows a statistically significant warming trend. The HadCRUT record shows a lesser trend as it doesn't include Arctic regions where the greatest warming occurs (Simmons 2010). To claim "no statistically significant warming" is to ignore the fully body of evidence.

"1. Statistically, and this is important unless you want to throw statistical analysis out with the wash, we have not warmed for the past 15 years."

Why do you insist on repeating the same incorrect information? Several people have now shown you that your assertion is incorrect. You are not being reasonable or discussing in good faith if you insist on repeating false statements and continuing to argue strawmen.

"3. Global cloud cover seems to have shifted upwards from a long downward spiral."

"In summary, while there is some consistency between ISCCP, ERBS, SAGE II and surface observations of a reduction in high cloud cover during the 1990s relative to the 1980s, there are substantial uncertainties in decadal trends in all data sets and at present there is no clear consensus on changes in total cloudiness over decadal time scales"

"Here we show that trends observed in the ISCCP data are satellite viewing geometry artifacts and are not related to physical changes in the atmosphere. Our results suggest that in its current form, the ISCCP data may not be appropriate for certain long-term global studies, especially those focused on trends".

Regardless of some people's wishful thinking, the planet continues to accumulate heat and warm.

And if the McLean you linked us to @64, is the same discredited McLean behind this awful and debunked paper, then citing "information" from his site is not helping your credibility either Camburn.

@Camburn:"Statistically, and this is important unless you want to throw statistical analysis out with the wash, we have not warmed for the past 15 years."
As the past decade has set temp. records, this claim rather shocked me, so I took the raw GISS data http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts.txt
and did a linear regression analysis for the past 15 years. The result? The slope is 0.0250 degreeC per year, with standard deviation 0.0027. This means that with a 95% confidence, the temperature increase over the past 15 years was between 0.02 and 0.03 degreeC per year. Or, the total increase over those 15 years was between 0.30 and 0.45 degreeC, with 95% confidence.
So Camburn, you are using different data? Could you share it with us?

Lindzen and Spencer's position makes sense. They think that in a warmer world, clouds will change to have a larger cooling effect than they do now. This _is_ a long term solution and it leads to a lower climate sensitivity than the IPCC give.

We could probably risk 1,200 ppm CO2 if their strongest hypothetical values are right.

I don't really want to go off on a tangent here, but even if cloud-feedback on climate-sensitivity were low as some hope, this would only apply to the increase of temperature, but it wouldn't prevent further ocean-acidification, would it?

So, from the "evil twin of climate change" point of view clouds don't really play a role. I often have the impression that ocean acidification is kept out of the limelight by "skeptics" as many of their lines of thought like cloud-feedback or geo-engineering don't help with that at all.

1: We have observations of CO2 and temperature for the past 130 years or so. We also have various satellite observations of temperature and cloud correlations for 30 years or so and sporadic visual accounts prior to that. These show that we are on track for a climate sensitivity of about 3 C.

2: We have proxy records of CO2 and temperature for hundreds of thousands of years (billions for some proxies). These consistently show a CO2 and temperature correlation, and the more recent / most solidly established fluctuations suggest a climate sensitivity of about 3 C.

3: We have climate models built on measured impacts of the physical and chemical processes impacting climate. These suggest a climate sensitivity of about 3 C.

Ergo, the 'skeptic' response is 'climate models cannot be trusted', 'proxy records are incorrect', and 'observed temperatures have just recently turned around and will now begin cooling rapidly'. That last being updated to a new turnaround date every ten years or so.

Just out of curiosity, is there a temperature point at which our local 'skeptics' would conclude they've made a mistake? Presumably if we hit a 3 C temperature anomaly within a few decades after doubling CO2 most (sadly I'm sure not all) would concede the point... but what about 2 C? Some claim climate sensitivity is only 1 C per doubling... but we're already over 0.8 C anomaly at 39% increase over the previous nearly flat CO2 level. At the current rate we'll pass 1 C this decade. Will that be enough to silence the 1 C crowd? Or will the 'temperature records are faked / unreliable' nonsense just be ramped up to cover?

On the flip side, if CO2 climbed to 420 ppm without temperatures breaking 1 C I'd start to think 3 C sensitivity might be a little bit high. If we got to 490 ppm without breaking 1 C then sensitivity would probably only be about 2 C.

All of this is 'fast feedback' sensitivity of course. On the multiple centuries scale we can expect another 50% or more warming over these figures.

"They think that in a warmer world, clouds will change to have a larger cooling effect than they do now."

Three points.

One, sorry but what they "think" is not good enough for me, and it should not be good enough for you either. Wishful thinking is not going to get us out of this mess.
Two, Lindzen says climate sensitivity for doubling CO2 is around +0.5 C, which suggests that a strong and negative cloud feedback should have kicked in after we warmed by about +0.5 C. The planet has not yet and we have warmed by over 0.8 C (for a 40% increase in CO2), and the rate of long-term warming continues at 0.15 to 0.2 C per decade.
Three, Spencer estimates climate sensitivity (for fast or Charney feedbacks) near +1.7 C. Over three times higher than Lindzen, and withing the range specified by the IPCC. So even Lindzen and Spencer are at odds....

I repeat my question from earlier. When is this alleged significant negative cloud feedback going to kick in? It did not kick in after +0.5 C warming as Lindzen's work suggests it should have. The mystic "iris affect" is now looking to be on as shaky ground as the long-debunked GCR fiasco.

"Just out of curiosity, is there a temperature point at which our local 'skeptics' would conclude they've made a mistake?"

Excellent question, and one that is likely to unanswered. These tactics employed by the "skeptics" are ultimately about delaying taking action. Spencer's estimate of +1.7 C for fast feedbacks will buy them is smarter than that of Lindzen, as it will buy them more time.

Lindzen is flat wrong, and the global SAT data (and work of Murphy and Trenberth et al.) have shown him to be wrong for many years now.

@Eric: " there is no GCR counter to AGW in the past 30 years, but there could certainly be GCR warming in the late 20th century or possibly recent GCR-based cooling offsetting some warming."

There is no indication this will happen, or that it will be significant enough to counter AGW. Until you provide some evidence, we'll have to remain skeptical about your unsupported claims.

"But GCR is not the story here, it is all the factors spelled out in How-we-know-the-sun-isnt-causing-global-warming.html which constantly fluctuate and add and subtract from the AGW warming. By not including them in either paleo studies or in the models that create clouds, we can't say anything about their effect on sensitivity. They can't be ignored just because they were canceled out over the past 30 years."

Which factors are you talking about, exactly?

It really sound as if you're grasping at straws here, like your fellow skeptics damorbel, Camburn and RSVP. I don't even know why we're arguing anymore, as you guys clearly have nothing.

Camburn @ 64... If you go back and read the Phil Jones interview you'll see that he says that it has warmed during that period at a rate of 0.12C/decade but is just short of the 95% statistical significance level.

So, I'm assuming having a 93% confidence level of warming for you means "no warming."

#78 archiesteel, Here's one link
www.utdallas.edu/nsm/physics/pdf/Tin_rev.pdf and there are many more. There are two points to consider, first that any of these factors in isolation can be "proven" to be a nonfactor over the last 30 years using linear trends. Second, combinations of these factors particularly with GCR will create enough warming and cooling to explain the paleo temperature record. The control knob for the ice age changes is GCR, with help from CO2 and solar factors. Since the solar factors are not considered in models and not part of the paleo record, they cannot be ruled out.

@Eric: again, I see no compelling evidence that such mechanisms could overcome the current anthropogenic warming. It seems to me you're suffering from wishful thinking here, and are not evaluating the science in an impartial manner.

"The control knob for the ice age changes is GCR"

Actually, Milankovitch cycles are the main culprits for ice ages, not GCR.

Sorry, but so far the evidence you've presented in favor of GCRs as a main driver of climate doesn't even come close to challenging the evidence against them.

archiesteel, can you point to some analysis that dismisses combinations of factors? Each one was dismissed in isolation in Dana's old thread, but that doesn't mean they can't combine in ways that radically change the climate. When you say "wishful thinking" are you implying that my scenario is impossible? Or just very unlikely?

I read this "debate" with a strong sense of deja vu. It could stand for any thread on climate change on any blog anywhere in the last ten years. An accurate description and analysis of one of the many lines of science associated with global warming. All of which are dismissed, one at a time, or in various combinations by a denier. The denier wants to ignore the obvious link between the known effects of CO2 in the atmosphere; the massive increase in CO2 in the atmosphere over the last 150 years, and especially the last thirty or so, as a demonstrated consequence of burning fossil fuels; and the rapidly rising temperatures and associated ecological and geographic consequences in exactly the same period.

Instead, ignoring all that, the denier has some pet theory that, by an incredible coincidence, just happens to produce exactly the same effects in precisely the same time period. I mean, it is just amazing that some other minor and hypothetical process could achieve that and give us the excuse to do nothing whatsoever about decreasing GHG emissions, isn't it?

Eric (skeptic)
it's not that in principle the GCR-climate relation is absurd. The problems is that there has been no clear evidence of the effect, let alone the 100 Kyrs periodicity needed to explain, or even contribute to, the glacial cycles. As far as we can tell, GCR contribution is small, at best.

Simply put, there is no evidence that your scenario is likely. I don't think you're looking at it skeptically enough, i.e. you seem ready to embrace a scenario which, based on the evidence we have, seems much more unlikely than the currently accepted science.

archiesteel@77:
Hadcrut data is the source. No.....I will change my statement.
Statistics are important. Either you work within the error bars or you don't.

I won't go into GISSTEMP and the errors of their Arctic measurements using the 1200K radius method. Prof Hansen will be correcting this I am sure. He is an honorable man.

Riccardo@85:
The evidence is mounting that CGR's do play a roll in climate.

00

Response: Note that the European Centre for Medium-Range Weather Forecasts (ECMWF) have independently determined that the HadCRUT record underestimates the warming record. They've created a reanalysis of Arctic temperatures using an entirely different method to GISSTemp, incorporating a range of sources including surface temperature measurements, satellites, radiosondes, ships and buoys.

Just watched a video last night, featuring Spencer claiming - since CO2 is such a small part of the atmosphere................. yawn. No I wouldn't bet on him being right.

Camburn
"After all, GAGW is still in the hypothosis stage and has not advanced to theory stage."

I'm not a scientist, but the way I understand the distinction is, that a theory is a hypothesis that has withstood the scrutiny of peer review. That would make every idea, the skeptics have, a hypothesis, and AGW a theory.

"Nicholls, a professor at Monash University in Victoria, Australia, said the IPCC 2007 Fourth Assessment report was subjected to several rigorous tiers of review. The study cites over 10,000 papers from the scientific literature, "most of which have already been through the peer-review process to get into the scientific literature."

"The report went through four separate reviews and received 90,000 comments from 2,500 reviewers, all of which are publicly available, along with the responses of the authors, Nicholls said."
by Stacy Feldman - Feb 26th, 2010 at Solve Climate dot.com

""After all, GAGW is still in the hypothosis stage and has not advanced to theory stage."

I'm not a scientist, but the way I understand the distinction is, that a theory is a hypothesis that has withstood the scrutiny of peer review. That would make every idea, the skeptics have, a hypothesis, and AGW a theory."

Something like that. Camburn clearly has a very limited understanding of what science is. What it clearly isn't is a linear progression of discrete ideas from hypothesis, to theory, to law. That would be silly. Silly enough that if that proposition were true, much of the infrastructure of modern civilisation would not work as it is based on scientific theory rather than scientific laws, of which there are remarkably few, especially outside of the domain of experimental physics.

Several people have showed you that HadCRUT data has a warming trend (about 0.12°C per decade) over the past 15 years. By now it's probably even statistically significant at the 95% confidence level, given that the quote from Jones was at the start of 2010, which has been the hottest year on record. And your insinuations about GISTEMP are just ludicrous. I know "skeptics" want us to just ignore the Arctic since it's experiencing the highest rate of warming, but I hate to break it to you - the Arctic is part of the globe too.

As others have noted, the evidence is mounting against a significant GCR impact on the climate. And frankly it's rather aggravating that people who want to be considered "skeptics" latch onto the GCR theory with such ferocity. The AGW theory has mountains of supporting evidence. The GCR warming theory has little supporting evidence and mounting contradictory evidence. A true open-minded skeptic would be able to see that the former theory is far more credible than the latter. Frankly anyone who rejects AGW and supports GCR warming forfeits the 'skeptic' label in my book.

@Camburn: "Hadcrut data is the source. No.....I will change my statement.
Statistics are important. Either you work within the error bars or you don't."

That doesn't even make any sense.

Look, it's simply. You claimed temperatures from 1995 to 2010 didn't show any warming. I clearly demonstrated you were wrong using the very same data set and web site.

There is no wiggling out of this one: you made a incorrect statement, I corrected you on it, and now I expect you to acknowledge you were wrong. Failure to do so will simply illustrate how you are not debating in good faith, but in fact are here to push junk science in order to further your political agenda.

dana1981
the ferocity, as you call it, is due to the fact that GCRs are the only way to have a sensitivity low to GHG but large to the sun. There are several good reasons why it can hardly be the case; the latest and largely unnoted is that the CLOUD experiment had contamination problems in the clean and controlled environment of their vacuum chamber. Immagine the dirty and uncontrolled real atmosphere ...

My unexemplary example of GCR is now sleeping ferociously. As I pointed out over and over, there are many such factors, celestial, lunar (tide shifts), solar (UV, x-ray, electric field effects, etc). Most of these affect clouds and weather. All are ignored by models. All are ignored by paleo studies. All can be individually shown to have no linear effect on temperature over the last 30 years. That leaves CO2 which is a very adequate explanation plus/minus PDO.

But this thread is about sensitivity and the role of clouds. The analysis of the last 30 years doesn't say a lot about sensitivity except that it varies. Right now we might be 2C per century, but maybe just 1C (considering that 1998-sized El Nino might have gotten us 0.1C above current temps). The sensitivity depends, in great measure, on those external factors. They could align and amplify CO2 warming, or damp it or do nothing as a whole. They are not very predictable. They are the wild card over the long run (with ocean cycles causing the short run fluctuations). Also they are independent of Lindzen/Spencer weather sensitivity.

We are dealing with scientific answers to scientific questions. Statements like this or that could happen, or they could cancel or they might be a factor or they amplify or they damp or they do nothing are all mere speculation that may be dismissed in the absence of any supporting evidence. And a long list of speculation does not increase the uncertainty associated with a scientific hypothesis.

"Right now we might be 2C per century, but maybe just 1C (considering that 1998-sized El Nino might have gotten us 0.1C above current temps)."

Sorry Eric but your line of thinking (i.e., extrapolating instantaneous rates of warming/cooling to the centennial scale) is just flat out wrong. In fact, the presence of transient internal climate modes and internal climate variability, solar cycles and volcanism are the very reasons why scientists look at long-term trends. Barton Paul Levenson has done some work on this and demonstrated that the standard deviation of the global temperature series plateaus when averaging over about 45 years, see here. The WMO and other groups use 30, and one could possibly get away with 20. There is no magic averaging window, because that itself in part depends on the nature of the data. For example, the time required to obtain statistically significant warming is shorter for GISTEMP than it is for CRU.

Lastly, even if we were trapped in a permanent El Nino, it would at most add +0.2 C to global temperatures each year, but that additional warming would not be integrated year-over-year-- ENSO (El Nino Southern Oscillation) does not represent a net gain of heat in the climate system, but a redistribution of heat within the system. It is possible that the additional warming of 0.1 to 0.2 C over and above the underlying warming trend may accentuate the warming by accelerating or enhancing positive feedbacks.....

If one looks at probability distribution functions of climate sensitivity (from multiple, independent sources), they are quite skewed towards higher temperatures, with a rapid drop off below 2.5C. Now that long tail to the right (higher sensitivity) is not necessarily an artifact of models, because it is present even for estimates of climate sensitivity derived using paleo and other data.

The surprises that may lurk in that tail of the PDF should be very sobering and very much reason for prudence and taking action. Fortunately, there is some relatively good news, Annan and Hargraveas estimate that the likelihood of climate sensitivity for doubling of CO2 (although we will very easily exceed doubling) exceeding about +4 C is highly unlikely, with other research by Annan indicating that +3 C is the most likely value.

To add to what Albatross said above... That 3C we get for a nearly assured doubling of CO2 puts us in uncharted territory with regards to tipping points. We will be well beyond the MWP. Well beyond the holocene maximum. We start having to look back millions of year, instead of thousands, for clues to what we may face.

You think there are uncertainties about how pronounced or extensive the MWP was just 1000 years ago? The Eocene is going to be a real bear to wrestle!

Eric #95 - you seem to be misunderstanding the concept of climate sensitivity. You're referring to it as 'warming per century', but that's not accurate - it's warming per a certain amount of radiative forcing. For example, if we double atmospheric CO2, the planet will warm approximately 3°C in response to the radiative forcing caused by the increased CO2 and associated feedbacks.

So the role of the feedbacks (mainly clouds and water vapor) are the issue at hand. But the climate sensitivity is pretty well constrained to 2–4.5°C for a doubling of CO2. The Lauer study I focused on in the article suggests that based on their cloud observations and model, it's more likely to be on the high end.

But when you're talking about warming per century, the factor you need to focus on is CO2, because it's the main determining factor regarding how much warming we'll see. If we double CO2, the feedbacks and sensitivity will tell us if the warming is 2 degrees or 4.5 degrees or something in between, but it's very likely to be somewhere in that range. To use Richard Alley's phrasing, CO2 is the main temperature control knob.

#96, muoncounter, there is a lot of supporting evidence that all the factors I have mentioned (and more) affect clouds. The evidence that is lacking is that these factors persist for a period of time long enough to affect climate. Also the link from cloud changes to climate is uncertain and tenuous in some cases. What is speculative is predictions. #97, Albatross, the decadal and centenial rates of warming are caused by the same factors. Obviously you are right that decadal doesn't scale to centenial due to short term factors like PDO. My point was just that sensitivity varies in addition to terrestrial weather like PDO based on external factors like GCR. One example is the high degree of blocking from local stratospheric warming from GCR spikes. That doesn't necessarily cause warming or cooling globally but it does alter the climate's sensitivity to CO2 warming for the period of time of the event.

#98 Rob Honeycutt, thanks for the comment. Tipping points are local, the ice can't melt unless the local temperature is warm. So they rely on a variety of local analyses, not "3C global" which means nothing locally. Last study I read, there were several plausible tipping points, mostly arctic. However, none of them would significantly affect worldwide temperature.

#99 Dana1981, my statement was a crude but realistic approximation based on the doubling of CO2 in a century. So if sensitivity is 2C and doubling takes a century, then the temperature increase is 0.2C per decade. I can very simply compare that estimate to various temperature measurements with the weather variation caveat above.